The H5N1 bird flu primarily affects and is highly contagious among birds and while there have been about 650 cases of humans who have been infected by the virus since it was discovered 17 years ago, the avian flu does not easily spread to humans. Humans rarely contract the disease and those who did were known to have been in close contact with dead and infected birds.

Still, it has been feared that H5N1 will evolve and become highly infectious to humans. In 2005, David Nabarro, then newly appointed senior UN system coordinator for avian and human influenza, said that health officials generally think that the risk of the bird flu virus jumping to humans is high. Now, a team of Dutch researchers has an overview on how this could be possible.

In a study "Identification, Characterization, and Natural Selection of Mutations Driving Airborne Transmission of A/H5N1 Virus" published in the journal Cell on Thursday, researchers from the Erasmus Medical Center in the Netherlands studied the ability of the H5N1 to attain airborne transmissibility between mammals.

They found that the virus is a mere five mutations away from being airborne-transmissible between ferrets. The ferrets were chosen for the study because the anatomy of their airway is similar to that of humans. Their bodies also respond similarly when infected with flu, making them good human proxies for lab studies.

"We found that as few as five [mutations] were sufficient to make the virus airborne," the researchers said. "For each of these five mutations, we have investigated exactly what the biological traits were that were associated with those mutations." The researchers, however, noted that it isn't clear whether the mutations would happen outside of the laboratory.

Study researcher Ron Fouchier, from the viroscience department of the Erasmus Medical Center, said that while the H5N1 may not cause a pandemic, the possibility of this happening should not be ignored.

To prevent H5N1 infection, health experts recommend avoiding contact with sick and dead poultry, as most of the humans who have contracted the virus had contact with H5N1-infected poultry. Travelers who visit affected countries are particularly advised to avoid live poultry markets as well as sick individuals who may have been infected with the H5N1. Handling and cooking poultry and eggs properly is also advised to avoid H5N1 virus infection.